Means for administration of medicines to human bodies for remedy and prevention of human diseases include a method of peroral or parenteral administration by the use of an injection, a pill, a capsule, a suppository, etc. and a method of endermic administration by the use of an ointment, a drug-containing adhesive plaster, etc. Among them, the endermic administration method has almost been disregarded up to the present except the direct application of external medicines, since the endermic absorption of a drug is extremely low. (This is especially because a skin physiologically has a biological barrier function against microorganisms, chemical substances, radioactive substances, heat, etc.) Recently, however, various external medicines for endermic application are being developed through recent progress of pharmaceutical technique.
In the conventional drug-administration method by the use of peroral medicines, injections, suppositories, etc., in general, the drug concentration rapidly achieves its peak and then decreases with the lapse of time, and therefore, it is difficult to maintain a constant concentration of the drug in the blood. Even the most conventional peroral medicines have various difficult problems including the induction of gastroenteric disorders, the inactivation of the drug during the initial passage through liver after the absorption thereof from the intestine, the induction of hepatopathy, etc., and the drugs which may fully satisfy the conditions for use as a medicine are extremely limitative. In addition, the injection also has various difficult problems including the use of a needle, the induction of immunoreaction which would be caused by the direct injection of a foreign substance, etc. Furthermore, this may bring on shock or the like dangerous state, since the removal of the drug once injected into a body by injection is almost impossible.
Under the circumstances, particular attention is recently being riveted to an endermic application method, which is free from the above-mentioned defects in the case of peroral or parenteral administration methods and which can maintain the relatively constant drug concentration in blood without any dangerous immunoreaction, and an ointment or a drug-containing adhesive plaster is used for the endermic application method.
In the endermic application method by the use of such ointment, drug-containing adhesive plaster or the like, the drug is required to be transferred from the skin to the capillary bed. Since the possibility of the passage of the drug through the corneal layer or keratin layer of epidermis depends upon the various properties of the drug, including the oil-solubility, the water-solubility, the drug concentration, the pH value, the molecular weight, etc., it was difficult to maintain the sufficient drug concentration in blood by the endermic administration method. In order to solve these difficult problems, a study on the base compositions for introducing the drug into the inside of the skin by means of chemical techniques has predominantly been carried out, which resulted in success of limited base compositions for only several kinds of medicines.